From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932923AbbA0Un7 (ORCPT ); Tue, 27 Jan 2015 15:43:59 -0500 Received: from smtp2.provo.novell.com ([137.65.250.81]:37667 "EHLO smtp2.provo.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932225AbbA0Un6 (ORCPT ); Tue, 27 Jan 2015 15:43:58 -0500 Message-ID: <1422391425.4604.7.camel@stgolabs.net> Subject: Re: [LKP] [mm] c8c06efa8b5: -7.6% unixbench.score From: Davidlohr Bueso To: Huang Ying , Peter Zijlstra Cc: LKP ML , LKML Date: Tue, 27 Jan 2015 12:43:45 -0800 In-Reply-To: <1422344736.24875.47.camel@linux.intel.com> References: <1420684064.6201.86.camel@linux.intel.com> <1420771673.12346.16.camel@stgolabs.net> <1420772606.6201.126.camel@linux.intel.com> <1420776122.12346.18.camel@stgolabs.net> <1422344736.24875.47.camel@linux.intel.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.7 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2015-01-27 at 15:45 +0800, Huang Ying wrote: > Hi, Davidlohr, > > Any update on this? The latest news I gotten is that you finally > reproduced this. The overall differences and cause of the issue is commit 37e9562453b (locking/rwsem: Allow conservative optimistic spinning when readers have lock). And since the performance issue occurs with writers-only, I'm fine with the degradation, we need to learn to live it. Real use cases will use mutexes instead. Also, the mentioned commit fixes a much more important problem than pathologically calling exec(2). Now, this doesn't mean we cannot do _anything_ about it. I sent a patcshet just a few days ago (sorry, I forgot to Cc you) that tries to minimalize (I've recovered ~75% of the regression) the writer penalties: https://lkml.org/lkml/2015/1/26/34 So all in all we don't really care for writer-only workloads, but hey, while we're at it. Thanks, Davidlohr